Compositions having isocyanate functional components are utilized in a variety of useful products such as adhesives, sealers, molded products and foams, which may be utilized in construction, vehicle manufacture, assembly of electronic subassemblies and devices, toys and the like. The adhesives have found widespread use because they provide reasonable processing conditions and exhibit good adhesion to many substrates, such bonding windows into structures, or parts to a structure. In automotive assembly plants windows are bonded in with one part adhesive compositions containing isocyanate functional components and a cure catalyst. One part adhesives cure as a result of exposure to moisture and are protected from moisture until applied to a substrate and the dispensing equipment is less complex than the equipment used to apply two-part adhesives. One part moisture curing adhesives known in the art are disclosed in U.S. Pat. No. 4,374,237, U.S. Pat. No. 4,687,533, U.S. Pat. No. 4,780,520, U.S. Pat. No. 5,063,269, U.S. Pat. No. 5,623,044, U.S. Pat. No. 5,603,798, U.S. Pat. No. 5,852,137, U.S. Pat. No. 5,922,809, U.S. Pat. No. 5,976,305, U.S. Pat. No. 5,852,137 and U.S. Pat. No. 6,512,033, relevant portions incorporated herein by reference and examples include BETASEAL™ 15630, 15625, 61355 adhesives available from The Dow Chemical Company, EFBOND™ windshield adhesives available from Eftec, WS 151™, WS212™ adhesives available from Yokohama Rubber Company, and SIKAFLEX™ adhesives available from Sika.
Two-part polyisocyanate based adhesives comprise, in one part, a polyisocyanate or an isocyanate functional prepolymer and in a second part a curing agent and catalyst for the reaction. Two part adhesives can be used for bonding replacement windows into vehicles, bonding parts together or parts to structures. Examples of such systems include the adhesive systems disclosed in the commonly owned U.S. Pat. No. 7,892,395; U.S. Pat. No. 6,965,008; EP 1433802 and EP 1578834, all incorporated herein by reference. The adhesives start to cure when the two parts are contacted and cure much faster than one-part adhesives.
Such products can undergo degradation in properties with use and exposure to natural elements, such as sunlight, humidity and thermal cycling. To reduce or prevent this from occurring stabilizers are commonly added to the formulations utilized to prepare cured polyurethanes. See for example Wu U.S. Pat. No. 6,512,033 and Zhu et al. United States Patent Application 2006/0270807 paragraphs 0043 to 0046.
Due to market conditions manufacturers of isocyanate based compositions may need to change ingredients utilized in the curable compositions (such as adhesives). Many compositions containing isocyanate functional prepolymers are sensitive systems in that changes in ingredients can alter how the adhesive compositions function or perform. Some ingredients such as fillers, plasticizers, thixotropes and the like when changed can impact how curable compositions function and the durability of the compositions. Such changes may result in stabilizer packages becoming ineffective in the altered composition.
Curable compositions that exhibit improved durability are desired. There is a need for compositions (e.g. adhesive) containing isocyanate functional prepolymers which have improved stabilizer packages to replace known stabilization packages which are found not to function properly, especially in compositions where ingredients (such as fillers and/or plasticizers) have been changed. Such compositions exhibit good durability in use and tests designed to predict long term durability. Cost effective systems for enhancing the durability of such compositions when exposed to environmental conditions, such as ultraviolet light, are needed.